Differential Diagnosis

Differential Diagnosis

Ronaldo C. da Costa & Curtis W. Dewey

Developing a comprehensive list of differential diagnosis is a key step in the diagnostic approach of patients with neurologic problems. This step is dependent on appropriate neurologic localization. For example, a dog with an abnormal gait in all four limbs could have a lesion in the cerebellum, brain stem, or cervical spinal cord. Obviously, the list of differential diagnoses and the approach for a patient with a cerebellar lesion will be quite different from one with a cervical spinal cord disease. Therefore to appropriately use the tables in this chapter, the clinician should complete a physical and neurologic examination to confirm that the patient has a neurologic problem and localize the lesion appropriately. When developing a list of differential diagnoses, the patient’s signalment and history often provide important clues. The goal of this chapter is to bridge the process of localizing a lesion with the selection of the most likely diseases to develop a diagnostic plan. Only the key features of the common diseases will be listed; more detailed information about the differential diagnoses included herein can be found in other chapters. The chapters containing detailed information will be indicated in each table.

Diagnostic approach

The approach to patients with neurologic diseases includes a thorough physical and neurologic examination aimed at localizing the lesion. Proper lesion localization is paramount for the diagnostic approach, as differential diagnoses and ancillary diagnostic tests are dependent on proper lesion localization (Fig. 4.1 and Fig. 4.2).


Figure 4.1 Algorithm presenting the differential diagnoses and diagnostic approach to brain problems according to the lesion localization.

CSM = cervical spondylomyelopathy. IVDD = intervertebral disc disease. FCEM = fibrocartilaginous embolic myelopathy. MRI = magnetic resonance imaging. CT = computed tomography. PCR = polymerase chain reaction. CSF = cerebrospinal fluid analysis.


Figure 4.2 Algorithm presenting the differential diagnoses and diagnostic approach to spinal problems according to lesion localization. (The Ohio State University. Reproduced with permission.)

*indicates nonpainful spinal cord diseases. CSM = cervical spondylomyelopathy. IVDD = intervertebral disc disease. FCEM = fibrocartilaginous embolic myelopathy. MRI = magnetic resonance imaging. CT= computed tomography. PCR = polymerase chain reaction. CSF = cerebrospinal fluid analysis.

In terms of lesion localization it may be helpful to localize the lesion to “big” regions first and then refine the process by narrowing the location to a specific brain or spinal cord region. For example, first establish whether the lesion is in the central (CNS) or peripheral (PNS) nervous system, then, if in the CNS, define whether it is the brain or spinal cord.

The brain can be functionally divided into forebrain (the same as thalamocortex, prosencephalon, or cerebrum), brain stem (mesencephalon or midbrain, pons and rostral and caudal medulla), and cerebellum. Vestibular signs are a very common manifestation of brain-stem disease. Vestibular disease can be a sign of a brain-stem problem (rostral medullary lesion) commonly known as central vestibular disease, or an inner ear problem (vestibulocochlear nerve or receptors), known as peripheral vestibular disease.

The spinal cord is divided into four major segments. It is important to remember that the spinal cord segments do not match up with the vertebrae in the cervical and lumbar regions and that there are seven cervical vertebrae but eight cervical spinal cord segments (Fig. 3.16). The main spinal cord divisions in terms of lesion localization are C1 to C5, C6 to T2, T3 to L3 and L4 to S3. In addition to these four classic spinal cord segments, there are three subdivisions that are clinically relevant and may assist the clinician in considering the appropriate differential diagnoses and select the most indicated ancillary tests. These subdivisions are the vertebral regions T2 to T10, and L6–L7–S1.

Finally, we have the neuromuscular diseases in a separate category. For detailed information on the clinical features seen with lesions in each specific brain, spinal, or neuromuscular region, the reader is referred to the specific chapters (Chapters 7, 13, 17, 18, and 19).

Differential diagnosis

The simplest approach to a case with neurologic signs, once the lesion is localized, is to consider differential diagnoses using the acronym lists based on pathophysiologic mechanisms. These acronyms are called either VITAMIN-D or DAMNIT-V and are very useful and practical ways to approach neurologic diseases. A list of common diseases according to the VITAMIN-D acronym is presented in Table 4.1 and Table 4.2, and Fig. 4.1 and Fig. 4.2. When using this acronym, it is useful to consider the signalment and history to develop appropriate differential diagnoses for the patient. For example, even though intervertebral disc disease is the most common spinal disease of dogs, it is not a reasonable differential diagnosis for a 6-mo-old dog with chronic paraparesis. Some generalities should be considered when using the VITAMIN-D acronym. Young dogs are more likely to have congenital or inflammatory conditions. Acute presentations are usually caused by vascular or traumatic conditions. Chronic presentations are usually seen with degenerative or neoplastic processes. Another way to approach patients with neurologic problems is to develop a list of diseases that are known to affect specific regions of the brain and spine. This is useful mainly for spinal disorders, because although many diseases affect several spinal regions (e.g. intervertebral disc disease, discospondylitis, fibrocartilaginous embolic myelopathy), many are region-specific (e.g. atlantoaxial instability, cervical spondylomyelopathy, degenerative myelopathy). The primary differential diagnoses for the most common diseases affecting each region of the brain and spine are presented in Tables 4.34.9. Some of the diseases listed are presented in only one table but can affect any region. For example, discospondylitis is more commonly seen in the lumbosacral area, but can affect any vertebral region.

Table 4.1 Common brain diseases based on the VITAMIN-D acronym for dogs and cats.

Disease mechanism Specific diseases
Vascular Canine or feline cerebrovascular disease (ischemic or hemorrhagic)*
Inflammatory/Infectious Meningoencephalitis of unknown etiology
Necrotizing meningoencephalitis
Granulomatous meningoencephalitis Infectious meningoencephalitides (bacterial, fungal, rickettsial, viral [distemper])
Trauma Craniocerebral trauma (head trauma, injury)
Traumatic vestibular disease (peripheral)
Toxic Lead poisoning
Metronidazole toxicity
Multiple toxicities cause brain signs (see Chapter 23)
Anomalous Hydrocephalus
Chiari-like malformation and syringomyelia
Quadrigeminal (arachnoid) cysts
Cerebellar hypoplasia
Cerebellar abiotrophy
Metabolic Hepatic encephalopathy
Hypoglycemic encephalopathy
Uremic encephalopathy
Electrolyte-associated encephalopathies
Idiopathic Idiopathic epilepsy
Idiopathic vestibular disease
Neoplastic Primary brain tumors
Secondary (metastatic) brain tumors
Nutritional Thiamine deficiency
Degenerative Cognitive dysfunction
Lysosomal storage diseases
Mitochondrial encephalopathies
Organic acidurias

*Bold used to indicate common diseases.

Table 4.2 Common spinal diseases based on the VITAMIN-D acronym for dogs and cats.

Disease mechanism Specific diseases
Vascular Fibrocartilaginous embolic myelopathy*
Epidural hemorrhage
Spinal cord hemorrhage
Inflammatory/Infectious Discospondylitis (bacterial or fungal)
Meningitis (steroid-responsive meningitis-arteritis or bacterial meningitis)
Meningomyelitis infectious (bacterial, fungal, rickettsial, viral) or noninfectious (unknown etiology, granulomatous meningoencephalomyelitis)
Spinal empyema
Vertebral osteomyelitis
Trauma Spinal trauma (fracture/luxations)
Traumatic disc extrusion
Traumatic atlantoaxial subluxation
Toxic None
Anomalous Atlantoaxial instability
Chiari-like malformation and syringomyelia
Arachnoid cysts
Multiple cartilaginous exostoses
Spinal bifida
Spinal dysraphism
Metabolic None
Idiopathic Disseminated idiopathic skeletal hyperostosis (DISH)
Neoplastic Primary or secondary spinal tumors
Nutritional Pathologic fractures due to metabolic bone disease Hypervitaminosis A (cats)
Degenerative Intervertebral disc degeneration
Degenerative myelopathy
Degenerative lumbosacral stenosis
Degenerative osteoarthritis of articular facets
Extradural synovial cysts
Developmental Cervical spondylomyelopathy

*Bold used to indicate common diseases.

Once the list of differential diagnoses is prepared for the patient, the most probable causes should be ruled in or ruled out, based on appropriate diagnostic tests. The diagnostic approach exemplifying the diagnostic tests used to confirm common brain and spinal diseases is presented in Fig. 4.1 and 4.2.

Specific brain regions

Forebrain (thalamocortex, prosencephalon, cerebrum)

Common diseases affecting the forebrain region mainly in small-breed dogs are the meningoencephalitis (any form of encephalitis), typically the noninfectious meningoencephalitides (granulomatous meningoencephalitis, necrotizing meningoencephalitis, or those where a specific diagnosis cannot be reached, so-called meningoencephalitis of unknown etiology). Neoplasia is also a common disease, mainly in dogs older than 5 yrs of age. Most dogs and cats have primary brain tumors, but secondary (metastatic) brain tumors are also seen. Head trauma can affect dogs of any age and size, and typically leads to forebrain signs in mild to moderate cases. Cerebrovascular disease (CVD) is being recognized more commonly in both dogs and cats. CVD develops as a peracute onset of typically strongly asymmetric signs. Table 4.3 lists the main characteristics of the primary differentials.

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Apr 7, 2020 | Posted by in SMALL ANIMAL | Comments Off on Differential Diagnosis
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